There are two types of comparison operators -- numeric and string --
which allow the user to specify the appropriate comparison function.
Suppose the segment name, which takes on a string value, contains the
names `11', and `8'. VMD cannot figure out if `8' should be less
than `11' (in the numeric sense) or greater than `11' (in the
lexographical sense). Instead of trying to resolve this problem
through some sort of internal heuristics, VMD leaves it up to the
user so that 8 < 11 but 11 lt 8. (Perl users should
recognize this solution.)

The numeric comparisons are the standard ones: <, <=,
= or ==, >=, >, and !=. The corresponding
string comparisons are: lt, le, eq, ge, gt,
and ne. As in perl there
is a ``match'' operator, =~, so that